1. Technical Field
This invention relates to optically isomeric inositol compounds and further to a process for preparing diols, or hydroxycarboxylic acids or their esters, all of optical activity, which have utility as intermediates or modifiers for the production of medicines or antibiotics. Such inositols result as intermediate products from synthesis of the optically active ultimate compounds.
2. Prior Art
Pairs of optical isomers exist which differ little in structure. Yet, despite their close similarity, one isomer of such a pair may be of great practical significance for example for medicinal use, and the other isomer may be ineffective. To selectively synthesize either desirable isomer of an isomeric pair, continued research has been made with a variety of asymmetric reactions. Now practically successful are several modes of asymmetric synthesis capable of high selectivity, say 95% or greater.
Certain asymmetric syntheses have heretofore been used for example for preparing hydroxycarboxylic acids or their esters. Details of these syntheses are described below.
In a publication entitled "Asymmetric Syntheses", Y. Inoue and H. Harada, Tokyo Kagaku-Dojin Co. (1973), there is reported an asymmetric reduction reaction for use in the synthesis of .alpha.-keto-esters. This known method is susceptible to reduced selectivity and hence decreased productivity.
A highly selective reaction of reduction is employed to derive optically active .alpha.-keto-amides as disclosed in and Bull. Chem. Soc., Japan, 62, p. 3598 (1989). In that instance, adverse racemization will often take place upon hydrolysis of the amide into an .alpha.-hydroxycarboxylic acid.
An oxidation reaction is taught for the synthesis of .alpha.-hydroxycarboxylic acids in J. Am. Chem. Soc., 107, p. 4346 (1985). As reported in J. Am. Chem. Soc., 106, p. 1531 (1984), .alpha.-keto-esters are produced through a reduction reaction in which an asymmetric coordinator is utilized.
The foregoing asymmetric syntheses of the prior art have the drawback that they tend to cause side reactions and objectionable racemization, thus involving low production yield and tedious optical resolution. This latter step of resolution is responsible for poorer productivity.